There are many big questions remaining in the world of molecular biology,
but some of the most important and most pressing relate to control of gene expression.
it's like,,,it comes down to the question; the issue of ..
DNA is the code of life ... What controls turning the DNA into flesh and blood?
One of the areas of control is DNA methylation. DNA methylation is changes to the DNA
that have nothing to do with the base sequence. This is not exactly a genetic change,
it is a change to the DNA. one of the aspects to this is that changes
to the DNA appear to permanent, not absolutely permanent,
but they follow the daughter cells, so that, the parent strand has modified DNA,
the daughter strands have the same modified DNA.
So it is like the changes follow the replication cycle.
so they are kind of permanent. let's turn our attention to the chemistry.
We have, ...let's look at this graphic... we have the cytosine/guanine base pair.
the cytosine is on this side, the guanine is on this side.
Across the top, this is in the major groove now,
we have a hydrogen acceptor, a hydrogen acceptor, a hydrogen donor
and then a methyl group right here.
DNA methylation is on the methyl group of the cytosine.
Let's turn our attention to...these models
are .... they are models of DNA,
but unlike other models, these models only show the major groove.
So this is our guanine/cytosine base pair and it can be turned over go ...
it is the same edge whether it is this way or this way.
If the guanine/cytosine is a dinucleotide, then the methyl groups are on the ends
and go on opposite sides.
So, these guys can be buried in the DNA in any, ...in any way you want.
When the guanine/cytosine dinucleotide is together it is a site for DNA methylation.
And we can see that the methyl groups are going to go on these green guys...
so if we put these little labels on them we can see that the methylation is on
the two outside units.
One of the important considerations of DNA methylation is that again,
the DNA methylation is permanent.
When the DNA is replicated, the base pairs are separated right down the middle
a new a base pair is added complimentary and so you say,"well, that is the end of that"
the DNA methylation goes away, but it doesn't.
There is a machine, an enzyme in the cell, in the nucleus, that automatically
and immediately goes through the new DNA and methylates the missing cytosine.
and the implications of this are that DNA methylation, it is sort of permanent
and it is even permanent through succeeding generations.
So, things that are known about DNA methylation:
It tends to go to cytosine/guanine dinucleotide.
There is GpC islands, they call them,
there's lots of guanine, cytosines in the promoter area,,,,
they do not seem to be methylated ....
dinucleotide GpC are methylated in vertebrates and plants,
but not so much in invertebrates.
The DNA methylation has to do with the histone modifications, histone being,
like the storage, like the packaging of the DNA .
When the dust settles though, the role of DNA methylation in
gene expression is not well understood.